Echo cancellation is used in telephony to remove echo from a communication in order to improve voice quality on a call. In addition to improving subjective quality, echo cancellation increases the capacity achieved through silence suppression by preventing echo from traveling across a network. Two sources of echo are relevant in telephony: acoustic echo and hybrid echo. Echo cancellation involves first recognizing the originally transmitted signal that re-appears, with some delay, in the transmitted or received signal. Once the echo is recognized, it can be removed by ‘subtracting’ it from the transmitted or received signal.